An investigation of the main factors that affect tear film stability in human and animal eyes is proposed. The study includes the identification and characterization of all major tear film components including those of the superficial lipid layer and the mucus layer coating the preocular surface. The interaction of tear film components with commonly used contact lens materials is included in the investigation. The effect of altered surface chemical conditions, e.g., high interfacial tension on the morphology and histology of the preocular epithelium will be studied. The relation between tear film irregularities and early histopathological in the epithelial ultrastructure will be investigated in rats on a vitamin A-deficient diet.